(1) Field of the Invention
The present invention relates to a dental treatment tool, particularly a gutta-percha remover for removing gutta-percha filled into a root canal.
(2) Description of the Related Art Including Info Disclosed Under 37 CFR 1.97 and 1.98
In dental caries treatment, an operation of cutting a patient's root canal, thereby removing an infected portion, forming it into an appropriate shape, and filling with gutta-percha and a sealer, which is used for filling in a gap between the gutta-percha and root canal wall, as a filler for prevention of subsequent reinfection is performed. Moreover, on the contrary to formation of a root canal, there are also cases where it is necessary to remove the gutta-percha and sealer (referred to as gutta-percha hereafter) filled in the root canal, and an operation of removing the gutta-percha is also performed. As a dental tool for removing the gutta-percha, a reamer or file has been applied since there is no conventional dedicated tool.
However, a problem as described below occurs if a reamer or file is used to remove the gutta-percha. In the case of removing the gutta-percha using a reamer or file, the reamer or file cuts and removes the gutta-percha so as to remove it through a screw-shaped groove of the reamer or file. While only the gutta-percha needs to be removed at this time, since the reamer or file has cutting power, there is fear that the root canal wall is also cut after the gutta-percha is removed, and drawn toward the root apex along with the gutta-percha. If the root canal wall is cut excessively, since a problem such as increase in likelihood of a fracture or perforation of the root canal occurs, it is best to leave healthy tissue as it is if possible.
On the other hand, while the root canal has straight line portions as well as various curved shapes such as spiral shapes, extremely curved shapes at the root apex, and the like according to the individual, there are also problems that the flexure of the reamer or file is not uniform along the length of the working portion and thus cannot follow the shape of the root canal exactly, all of the gutta-percha cannot be removed from the root canal, and the curvature in some instances exceeds the limit, breaking the tip of the tool.
In other words, if the file does not curve uniformly along the length of the working portion, there is an inconvenience that the working portion of the file touches only one side of the curved portion of the root canal and not the other side, some of the gutta-percha remains, and stress concentrates on the tip, thereby fracturing it.
The cross-sectional area of the reamer or file cut orthogonal to a rotational axis of the working portion becomes smaller as it approaches the tip in the same ratio as the tapering ratio of the working portion. With such a structure, it is easy to bend at the tip of the working portion and difficult to bend at the base end of the working portion. Moreover, this is a structure that space (gap between the gutta-percha and the root canal wall) for moving the removed gutta-percha becomes smaller, thereby making it difficult for the gutta-percha to be removed.
In Patent Document 1 (JP Patent No. 3731187), endodontic equipment including tissue removal edges provided unequally spaced on the periphery of a shaft is proposed as an improvement of the above situation. These tissue removal edges can give a more uniform cutting force inside and outside the curvature of the root canal than a conventional symmetrical tool that easily cuts the inside of the curvature of the root canal by a force working on the root canal wall at the curve by the tool.
In Patent Document 2 (JP Patent Publication No. 2002-253578A), a dental reamer having a cross-sectional shape created by cutting along two lines and twisting it such that the center of a circle and two arcs are left is proposed. Such a shape allows improvement in compliance to the curvature of the root canal by increasing flexibility compared to the conventional tool as well as decreasing cutting performance.
In Patent Document 3 (JP Patent Publication No. 2001-170076A), a dental root canal tool including a file with a cross-sectional shape constituted by an arc and a chord is proposed where L is (⅝)D or greater when L is height of the cross section connecting the midpoint of the vertex of the arc and the chord, and D is diameter of the arc. Such a structure allows high flexural rigidity and flexural strength, thereby allowing creation of a path for a reamer or a file ahead of time by penetrating into the root canal.
In Patent Document 4 (JP Patent Publication No. 2000-83968A), the cross-sectional shape of the working portion of the file is oblong. Moreover, an oblong aspect ratio that changes along the length (axial direction) exhibiting different flexibilities is proposed. It utilizes the fact that flexibility increases if the aspect ratio is increased.